A Computational Fluid Dynamics Study of Particle Penetration through an Omni-Directional Aerosol Inlet

Abstract

Computational fluid dynamics (CFD) was used to study aerosol penetration through the entrance section of a bell-shaped omni-directional ambient aerosol sampling inlet. The entrance section did not include either an insect screen or a large-particle pre-separator. Simulations of the flow field were carried out for wind speeds of 2, 8, and 24 km/h and a fixed exhaust flow rate of 100 L/min; and, particle tracking was performed for 2 to 20 μ m aerodynamic diameter particles. Penetration calculated from CFD simulations was in excellent agreement with experimental results from previous studies with the root mean square relative error between simulation and experimental data being 3.8%. CFD results showed that the most significant regional particle deposition occurred on the upwind side of a curved flow passage between two concentric axisymmetric shells of the inlet housing and that deposition at the leading edges of the shells and within the exhaust tube was far less significant. At a wind speed of 2 km/h, penetration was affected by gravitational settling, e.g., penetration of 20 μ m particles was 71.9% when gravity was included and 80.4% without gravity. At higher wind speeds gravity had little effect. An empirical equation was developed to relate aerosol penetration to a Stokes number, a gravitational settling parameter, and a velocity ratio. Good fits of the correlation curves to experimental data and numerical results were obtained.

Financial support for this study was provided under US Army contracts W911SR-07-C-0056 and W911SR-08-C-0019. The authors are grateful to Drs. Edward Stuebing and Jerold Bottiger at Edgewood Chemical and Biological Center for providing guidance and support for research activities carried out under these contracts. The authors also thank Dr. Shishan Hu and Dr. Sridhar Hari for valuable discussions on CFD simulation, and Messrs. Rohit Nene and Michael Baehl for their previous efforts in wind tunnel testing.